Your absolutely right Mike, I used a lighter on it and low and behold smelled the tar coming off of it. My son will be dissapointed, but I am happy to say that there is a good possibility that he's now hooked. Thanks for you reply.

I might add that, although one tends to think of tar as man-made, it can occur naturally as:

- a consequence of oil (especially thick oil) exuding into the sea and eventually getting washed ashore

- layered deposits, seeping or not depending on its viscosity.

And when one finds tar balls on the beach, they may have come from ships, oil spills or natural seeps - it would not be obvious which.

In a similar way, lumps of concrete (especially old, say Roman, concrete) can be mistaken for rock.

So it is entirely reasonable for a rock hound, upon seeing what appears to be a lump of tar, to pick it up for inspection. No shame in that.

Also, tar is an interesting substance in terms of its material properties (rheology, in relation to rocks). One can learn about geological deformation processes from studying it. Pitch (related to tar) is a rare substance in that its viscosity varies greatly with strain rate. That is: if you leave a piece of pitch alone at room temperature, it will slowly flow under its own weight (low strain rate), but it you hit it with a hammer (high strain rate) it will shatter.